DP83867E: DP83867IR - center tap of RJ45 with pulse trans

Alan Zha

Part Number: DP83867E

Is DP83867E a current-mode or voltage-mode line driver?

If it is a voltage-mode driver, then the voltage reference must be GND. Right? Is it necessary to wire the voltage reference (GND) signal along with each line driver signal pair (TD_P and TD_M) between the PHY and magnetics like this:

TD_P_A TD_M_A GND TD_P_B TD_M_B GND TD_P_C TD_M_C GND TD_P_D TD_M_D GND

Thanks!

over 7 years ago

0 Ross Pimentel over 7 years ago

TI__Mastermind 23675 points

Hi Alan,

The DP83867E is a voltage mode driver.
You need to connect the center tap to ground through a 0.1uF decoupling cap.
Please see figure 26 (page 92) in the DP83867E datasheet.
Also, the center taps are not allowed to be shorted together.

0 Alan Zha over 7 years ago in reply to Ross Pimentel

Prodigy 105 points

Figure 26 of the DP83867E datasheet has 2 ground connections. I think the two should be different. The one to the left DP83867 side should be DP83867 signal ground and the one to the right RJ-45 should be the chassis ground. Right?

0 Ross Pimentel over 7 years ago in reply to Alan Zha

TI__Mastermind 23675 points

Hi Alan,

You are correct. Most use a separate grounds to eliminate ground loops and to maintain isolation.

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DP83867E: DP83867IR - center tap of RJ45 with pulse trans